So, a friend of mine here at work asks me a great question about if “their friends can visit Korea without a travel visa” from the United States. Well, the answer is:
If they don’t stay for more than 30 days. Supposedly, U.S. citizens with valid visas can travel into South Korea without a visa up to 30 days. If they plan to stay for more than 90 days, they need to get a working visa or suitable alternative. More details here.